Tiny galaxies bursting with stars

A near-infrared image captured by the Hubble Space Telescope reveals 18 tiny galaxies that existed 9 billion years ago and are brimming with starbirth. The numbers show you where the thumbnail galaxy pictures are located in the wider picture.

The Hubble Space Telescope has turned up a population of tiny, young galaxies that are just brimming with starbirth.

The 69 dwarf galaxies were spotted during a three-year sky scan known as the Cosmic Assembly Deep Extragalactic Legacy Survey, or CANDELS. Their average mass is only about 1 percent the mass of our own Milky Way galaxy, but they're churning out stars at such a furious pace that the stars are on track to double in just 10 million years. It would take the Milky Way 10 billion years to achieve a similar doubling.

The galaxies are being seen as they existed 9 billion years ago, during a time when the star production rate was higher than it is today. But even by that measure, the birth rate is so high that astronomers may have to reassess their models for galaxy formation.

Astronomers could spot the galaxies because the radiation from hot, young stars lit up the oxygen in the gas surrounding them like a neon sign. Or at least that's the way it's described in today's image advisory from NASA.

"The galaxies have been there all along, but up until recently astronomers have been able only to survey tiny patches of sky at the sensitivities necessary to detect them," said Arjen van der Wel of Germany's Max Planck Institute for Astronomy, lead author of a paper on the results being published online Nov. 14 in The Astrophysical Journal. "We weren't looking specifically for these galaxies, but they stood out because of their unusual colors."

This video zooms in on Hubble imagery showing tiny galaxies that are brimming with star formation.

A co-author of the paper, Amber Straughn of NASA's Goddard Space Flight Center, said the spectral signature of the oxygen was a tip-off that the galaxies were in the throes of extreme starbirth. "Spectra are like fingerprints. They tell us the galaxies' chemical composition," she explained.

The Hubble team said the observations appear to be at odds with recent detailed studies of the Milky Way's satellite dwarf galaxies. "Those studies suggest that star formation was a relatively slow process, stretching out over billions of years," said Harry Ferguson of the Space Telescope Science Institute, co-leader of the CANDELS survey. "The CANDELS finding that there were galaxies of roughly the same size, forming stars at very rapid rates at early times, is forcing us to re-examine what we thought we knew about dwarf galaxy evolution."